The proposed research project has been designed to study uric acid transport in rat kidney with in vivo and in vitro methodology. Free flow micropuncture tenchniques will be employed to assess segmental uric and transport along the length of the nephron. Transport will be evaluated under carefully controlled variations in extracellular fluid volume and sodium balance. In addition, studies have been designed to assess the relationship, if any, between glucose and hydrogen dependent sodium flux and uric acid transport within the proximal tubule. In vitro studies have also been proposed to study urate transport in luminal and contraluminal membrane vesicles of rat renal cortex, prepared with the techniques of differential centrifugation and free-flow electrophoresis. These studies should permit an analysis of the mechanism of urate transport across the isolated membranes and should allow an evaluation of the possible pH, electrolyte and solute dependence of urate transport.